The present invention relates to automobile electronic control systems, and relates more particularly to a method and system for providing real-time estimation of the trajectory of a vehicle that is equipped with an Electronic Stability Program (ESP).
At present, automobile engineers and manufacturers are designing and implementing vehicle trajectory estimation systems that calculate and store data from which the trajectory a vehicle takes during travel can be estimated and reconstructed. Accurate vehicle trajectory estimation can be used in vehicle performance testing and accident reconstruction, among other applications. Typically deployed vehicle trajectory estimation systems utilize either an external signal communication infrastructure, such as the Global Positioning System (GPS), or specialized additional equipment such as gyroscopes, accelerometers and wheel tachometers that directly measure wheel dynamics. The systems which use an external signal communication infrastructure determine vehicle position in approximate real-time via a process of triangulation based upon varying reception times of radio waves broadcast by various GPS satellites and/or cellular antennas operating in the region of the vehicle. It has been found that the update rates of such systems can be too slow for precise continuous trajectory estimation. In addition, the position accuracy provided by such systems may be too low depending on the level of precision required, and signals may be corrupted, discontinuous or unavailable due to contingencies such as presence of tunnels and extreme weather conditions. Furthermore, systems that use additional measurement equipment often suffer from inaccuracies due to sensor drift and sensor output bias.
Recently developed automobile safety systems such as Anti-Lock Braking Systems (ABS) and Vehicle Dynamics Control Systems (VDC, also known as Electronic Stability Program (ESP)) have been incorporated in many automobile models. As the article xe2x80x9cVDC, The Vehicle Dynamics Control System of Boschxe2x80x9d by A. van Zanten et al. (1995) describes, Vehicle Dynamics Control systems are equipped with sensors that detect various primary dynamic parameters, such as the yaw rate ({dot over ("psgr")}), the lateral acceleration (ay), and wheel speed (vwh), as well as driver-controlled parameters such as the steering wheel angle and the brake pressure. From the detected primary parameters, an Electronic Stability Program (ESP) estimates various quantities pertaining to the real-time dynamics of the vehicle, and from these quantities, determines whether to implement automatic controls. For example, during certain unsafe driving conditions, such as a sharp turn on a slippery surface, the ESP may determine from the estimated vehicle dynamics that special control measures are necessary for lateral and longitudinal stability of the vehicle. In such cases, the ESP automatically activates engine and/or brake elements which alter the dynamics of the vehicle so as to increase vehicle safety.
In accomplishing the complex adjustments involved in adapting to various unsafe driving conditions, the ESP derives and estimates using the primary detected parameters, several dynamics parameters that are not readily measured by available sensors, such as the longitudinal acceleration of the vehicle, wheel-to-surface friction coefficients, wheel slip angles and slope angles. Since ESP controller sampling rates are on the order of 50 Hz, vehicle dynamics parameter estimates can be updated in near real-time. In addition, the ESP uses feedback from the derived estimates to correct for drift in the sensors and for additional bias due to sloped road conditions.
It is known in the art that a vehicle""s trajectory over time can be calculated as a function of the vehicle dynamics parameters if there is a full and accurate set of parameters for each near-instant of time. Given the high accuracy provided by the self-correcting mechanisms in ESP systems, and the relatively fast sampling rate at which ESP controllers make direct measurements and derive estimates of the vehicle dynamics parameters, it would be advantageous to selectively harness the capabilities of the ESP in order to generate a continuous vehicle trajectory estimation.
It is therefore an object of the invention to estimate the trajectory of a vehicle equipped with an Electronic Stability Program (ESP) using the dynamics parameter detection and estimation functions provided by the ESP.
In accordance with the desired object, the present invention provides a method for estimating a trajectory of a vehicle equipped with an ESP under both normal and abnormal driving conditions, such as wet or icy roads, sharp turns at high speed, uneven terrain, etc. According to the method, sensor data pertaining to the dynamics of the vehicle is obtained, and an estimate of the trajectory of the vehicle is calculated based upon the sensor data and estimates of vehicle dynamics parameters made by the ESP. The acquisition of the input data and the calculation of the estimates are performed independently of any external signal communication infrastructure-based trajectory estimation tools.
In an exemplary embodiment, the sensor data is communicated by sensors that are readily available in commercial vehicles, such as a yaw rate sensor and a lateral acceleration sensor. The sensor data, comprising input data to the ESP, forms the basis for estimation of a wide range of vehicle dynamics parameters that are either not readily measurable in the vehicle (such as the longitudinal acceleration), or cannot currently be directly measured in the vehicle (such as wheel coefficients of friction, wheel slip angles, etc.). These estimated vehicle dynamics parameters are in turn used to compute the real-time position of the vehicle with respect to a stationary reference frame.
The method according to the present invention also increases the accuracy of trajectory estimates by providing for high sampling and update rates, and by compensating for sensor drifts using observed dynamics parameter estimates computed by the ESP. The fast sampling rates allow real-time computation of the vehicle trajectory, up to the limit of the ESP controller cycle, thereby providing a sampling rate adequate for the bandwidth of vehicle motion even in extreme driving conditions.
In addition, the present invention provides a procedure for obtaining the trajectory of a vehicle. According to a first embodiment, a vehicle equipped with an ESP obtains sensor data for an instant in time, computes related vehicle dynamics parameters, and from these data sources, estimates the position of the vehicle at that instant in time. The estimated position is then recorded either internally or externally. The trajectory is then assembled from the time series of recorded positions, which time series has a total duration T.
According to a second embodiment, a vehicle equipped with sensors (with or without an ESP) obtains and records sensor data at a number of instants of time over a duration T. The recorded sensor data is thereafter input to an ESP which may be internal or external to the vehicle. The estimation of vehicle dynamics parameters and the calculation of positions may occur in near real time, while the vehicle is in operation, or it may occur subsequently, when the vehicle is no longer in operation.
The method and system for vehicle trajectory estimation provided by the present invention can be advantageously used in numerous applications including, but not limited to: vehicle accident reconstruction, various testing of vehicle maneuverability and maneuver reconstruction, a stand-alone vehicle tracking system and/or an enhancement to future GPS systems that may have faster sampling rates and higher accuracy. When used in conjunction with GPS systems, the method and system of the present invention can be particularly advantageously applied when GPS updates are lost due to, for example, severe weather conditions, or driving in tunnels. Moreover the present invention can be usefully applied to pre-defined trajectory tracking for autonomous vehicles. By pre-defining the trajectory, the ESP can use the inverse of the equations used to compute the trajectory to calculate the dynamics parameters required to control the vehicle to follow the pre-defined trajectory.